Calorie restriction diet extends life of monkeys by years

Put down the cake. Going on a permanent diet could make you live longer, if findings from monkeys hold true for people.

A long-running trial in macaques has found that calorie restriction makes them live about three years longer than normal, which would translate to about nine years in people.

Such a strict diet might not be for everyone, but understanding the mechanisms behind any benefits of calorie restriction may one day lead to anti-ageing medicines, says Julie Mattison at the National Institute on Aging (NIA) in Baltimore, Maryland. “The goal is to improve human health,” she says.

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Many studies have shown that calorie restriction extends lifespan for lab organisms, from yeast through to worms, flies and mice. This has prompted a few thousand people to choose to restrict their calories to between 1500 to 1800 kcal a day (women and men are usually advised to consume 2000 and 2500 kcal, respectively). Their hope is it will give them longer and healthier lives, and there’s some evidence that such people have better blood cholesterol and glucose levels.

Age record breakers

But it’s unclear if the approach can really lengthen the lives of long-lived animals like us. Two trials of calorie restriction in macaques, which live around 26 years in captivity, have until now produced conflicting results.

Now the teams have compared their most recent results and their analysis backs the earlier trial that had positive findings. The NIA study, on the other hand, had several problems, including issues with some of the control monkeys eating fewer calories than expected, and some of the animals beginning their restricted diet as juveniles – which reduces lifespan.

Even so, in the NIA trial, four of the monkeys that began the diet as adults lived to be over 40, breaking all known records for macaques – an observation which may cheer those who practise calorie restriction. However, picking out single results like this from a larger study isn’t good evidence, says Mattison.

Side effects

In the Wisconsin trial, animals did live significantly longer than controls – calorie-restricted males lived about two years longer, while calorie-restricted females lived about six years longer. There were also lower rates of heart disease and cancer in these monkeys. These are the major causes of death in people, lending support to the idea that the results apply to humans, says Luigi Fontana of the University of Brescia in Italy.

However, Brian Delaney, who is president of the Calorie Restriction Society, an organisation that supports the practice in people, says some who follow this diet are disappointed by the relatively modest benefits in monkeys compared with mice, which have lived up to 50 per cent longer than normal.

“Is it worth it?” asks Delaney. “My choice is to do it. But I’m so used to the diet that it really isn’t very difficult for me anymore.”

Delaney has been practising calorie restriction for 24 years. Until someone is used to it, the diet involves planning every meal with precision, and side effects can include feeling cold and reduced libido.